The present invention relates to an apparatus for bracing a plurality of vertebrae of the human spine.
Known supporting means operate with so-called lamina hooks which are disposed on a threaded rod. A compressing means is disclosed in British patent 2 131 300. A distracting means is disclosed in U.S. Pat. No. 4,382,438. The threaded rod bridges a plurality of vertebras and is not suited to act on vertebras which are disposed between the lamina hooks. Before using the supporting means a distraction or, respectively, compression has to be provided by means of an additional device.
German 90 06 646 U1 discloses an apparatus in which a lamina hook is replaced by a clamp-shaped holding member having a pair of legs of which one can be bent with respect to the other. Thereby the giapophysis of the vertebras may be used as anchoring points for the compressing and distracting apparatus.
German 88 02 112 U1 teaches a supporting device for the human spine, according to which the so-called pedicle screws are screwed in the pedicle body of the vertebras. The pedicle screws cooperate with tensioning means which bridge across one or more vertebrae to introduce forces between the vertebrae. The known device affords a primary stabilization of the vertebrae with respect to all degrees of freedom. However, when a number of vertebrae of a non-traumatic spine for example, are to be repositioned, separate means necessary to perform the reposition before the known supporting device may be effectively used.
WO 91/01691 discloses an apparatus for bracing vertebras of the human spine, comprising pedicle screws having slotted heads to receive a rod. The legs of the slotted screw heads include an outer thread on which a nut is screwed which contacts the rod to fix a predetermined position.
EP 0 443 892 discloses a similar device comprising a pedicle screw, the slotted head thereof including internal threaded portions for receiving a fixing screw which is brought into engagement with a serrated or similarly roughened rod to fix the relative position of the rod and the individual pedicle screw. A ring disposed around the head of a pedicle screw is provided so that the legs of the screw head do not spread apart while fixing the rod, as otherwise the engagement between the fixing screw and the screw head may be lost. A similar apparatus is disclosed in WO 90/09156.
Again, the devices last mentioned require separate means for repositioning, thus being suited to maintain a repositioned condition, but not suited to perform repositioning.
It is an object of the present invention to provide an apparatus which is suited to reposition the vertebrae of the human spine as well as to support the vertebrae in the repositioned position thereafter.
The objects are solved by the apparatus of the invention.